This is a fine exposition of some of Clifford's main ideas and also a fine instance of his power to develop some clear explanation of the most abstruse scientific conceptions; but the reader should be aware that some portions are a blend of the author's ideas and that of Karl Pearson, a portion of the book being written by the latter (Clifford died with the book infinished). To have a better idea of Clifford's insights, see his Lectures here at archive.org